The finding comes from Chukuka S. Enwemeka, PhD, and colleagues at New York Institute of Technology. Their study was funded by Dynatronics Corp., which makes the blue-light device used in the study.

In earlier studies, Enwemeka's team found that MRSA died when exposed to blue light that included part of the ultraviolet (UV) spectrum. Even though the total UV dose was less than that of a few minutes of sunlight, it would be safer not to expose humans to any more UV light than necessary.

So the researchers used a LED device that emits blue light not in the UV spectrum, and found it worked nearly as well.

"Irradiation with [blue] light energy may be a practical, inexpensive alternative to treatment with pharmacologic agents, particularly in cases involving cutaneous and subcutaneous MRSA infections," Enwemeka and colleagues conclude.

The researchers tested two MRSA strains: one typical of the strains that bedevil hospitals, and one typical of the strains found in the community. Both strains were susceptible to the blue light.

Relatively low doses of blue light -- about 100 seconds' worth -- killed off about 30% of MRSA in laboratory cultures. Longer doses were more effective, although with diminishing returns. It took about 10 times longer exposure to kill off 80% of the MRSA in culture dishes.

Exactly how blue light kills MRSA, or whether the bacteria can become blue-light resistant, isn't known.

The study will appear in the April 2009 issue of Photomedicine and Laser Surgery.